The present invention relates to an image formation unit used in a copier, a facsimile machine or a printer and to an image formation apparatus which includes this image formation unit.
In recent years, market demand in relation to the performances of image formation apparatuses such as recording speed, resolution and rise time has diversified and various types of image formation apparatuses which differ in these performances are required. However, as the diversified apparatus types appear, the number of the types of necessary components and units increases.
In addition, time for a user to change desired performances has recently become shorter. Specifically, time for a user who purchased an image formation apparatus of a certain type to obtain an image formation apparatus of another type because the user could not correctly recognize the quantity of print output at the time of purchase or the quantity of print output changes from that when the user purchased the apparatus, has become shorter.
According to a conventional image formation apparatus, if the above instance occurs, a user disadvantageously needs to purchase another image formation apparatus, which imposes heavy burden on the user. Further, on the manufacturers"" side, if many types of apparatuses are produced, manufacturing cost is disadvantageously pushed up.
On the other hand, the image formation apparatus such as a copier or a printer is required to be subjected to maintenance operations frequently while the apparatus is used. This is because image formation processes are carried out while preserving a delicate balance, and it is necessary to adjust the balance between the components of the apparatus to ensure good image formation. The maintenance operations are required due to, for example, the fact that if low quality paper is used, paper particles adhere to a photosensitive member to make it impossible to ensure good image formation or due to the degradation of rubber members.
As for an image formation unit around a photosensitive member which unit is provided to realize an electrophotographic method, in particular, a maintenance operation is highly demanded so as to make the best use of the performances of the unit. Conventionally, the image formation unit of the photosensitive member or the like used in an image formation apparatus is shorter in life than the image formation apparatus. It is, therefore, necessary to replace the image formation unit by a new one several times while one image formation apparatus is used. The image formation unit has a shorter life because of a phenomenon that the photosensitive member is worn because of the impact of, for example, a cleaning blade on the photosensitive member or, if the apparatus of a two-component development type is used, because of a spent toner phenomenon that a toner adheres to a carrier after the apparatus has been used for a long period of time to thereby deteriorate the charging performance of the unit or the like.
As a result, it is necessary to carry out maintenance operations including the repair or replacement of the image formation unit while the image formation apparatus is used. The maintenance operations are roughly divided into maintenance centered around repairs made by engineers such as manufacture""s service persons and that centered around replacement made by the user himself.
In the maintenance on the part of service persons or the like, the image formation unit is also repaired if possible and the quantity of waste to be disposed of can be advantageously reduced. On the other hand, the maintenance disadvantageously generates time or so-called downtime for which the user cannot use the image formation apparatus before a service person returns the apparatus to the user. In the context of the field of printers which is particularly widening or the overseas sales of printers, there is fear that maintenance operations cannot be conducted to image formation apparatuses at sufficiently earlier time because users outnumbers service persons or the distance from a service center to the user is long.
Meanwhile, there is conventionally known, as an image formation apparatus enabling a user to carry out maintenance operations, a process cartridge type image formation apparatus in which a photosensitive member is formed integrally with a development device and the integrated photosensitive member and development device are detachable from the main body of the image formation apparatus. Since the photosensitive member and the image formation unit such as a development device are formed integrally with each other, the process cartridge type image formation apparatus has an advantage in that the user can easily carry out a replacement operation if the life of the cartridge ends. The process cartridge type image formation apparatus has, however, disadvantages in that since a plurality of image formation units are formed integrally, it is necessary to replace the entire cartridge even if the life of a part of the image formation units ends, cost is pushed up and heavy burden is imposed on the environment. As more attention has been recently paid to the environment, the recycle of process cartridges is underway. However, since the user can easily detach the process cartridge, some process cartridges are disposed of without being recovered, whereby the complete recovery of process cartridges is not realized.
As explained above, according to the conventional image formation apparatus, the image formation unit is almost a consumable supply in the sense that unless maintained, good image formation cannot be ensured for a long period of time and, therefore, the problem arises as to how to carry out various maintenance operations.
In this specification, an image formation unit which can be replaced by another unit and attached to an image formation apparatus will be referred to as xe2x80x9cimage formation unitxe2x80x9d and the sections of the image formation apparatus other than the image formation unit will be referred to as xe2x80x9cimage formation apparatus main bodyxe2x80x9d hereinafter unless otherwise specified. In addition, if a plurality of image formation units exist in an image formation apparatus, only the noted image formation unit will be referred to as xe2x80x9cimage formation unitxe2x80x9d and the image formation units other than the noted image formation unit and the sections of the image formation apparatus other than the image formation units will be collectively referred to as xe2x80x9cimage formation apparatus main bodyxe2x80x9d hereinafter.
Thanks to the recent technological innovation made by the applicant of the present invention, the lives of respective constituent members of an image formation apparatus are steadily lengthened. For example, the applicant of the present invention succeeded in developing a technique of lengthening the life of a photosensitive member the performance of which has been conventionally difficult to maintain until the life of an image formation apparatus ends. Such technological innovation enables the life of an image formation unit to be equal to that of an image formation apparatus main body or to nearly surpass the life of the image formation apparatus main body.
If the life of the image formation unit is longer, the number of times of necessary maintenance operations, quite naturally, decreases. If the number of times of necessary maintenance operations decreases, a service person can arrive at a user in short time after the service person receives a maintenance request from the user and the burden of maintenance on the user decreases, accordingly.
If the image formation unit, in particular, has a comparable life to that of the image formation apparatus main body and the image formation unit as well as the image formation apparatus which has been used is recovered when the user purchases or rents a new apparatus or the like, then it is possible to dispense with a maintenance operation.
If the life of an image formation unit is longer, it is considered that one image formation unit is recycled (reused) to be used with a plurality of image formation apparatus main bodies. If it is assumed that the life of an image formation unit is three times as long as that of an image formation apparatus main body, it is possible to use the image formation unit with three image formation apparatus main bodies without the need to carry out any maintenance operations. In addition, if the life of an image formation unit is shorter than that of an image formation apparatus main body and the user parts with the image formation unit before the end of the life of the unit because the performances of the image formation apparatus which the user requires change in a short period of time, then this image formation unit can be used with another image formation apparatus main body.
Nevertheless, even if it is possible to reuse an image formation unit, the image formation unit detached from one image formation apparatus cannot be reused with another type of an image formation apparatus. This is because image formation units have been conventionally manufactured for each type of an image formation apparatus (or for each type of an image formation apparatus main body).
Japanese Patent Application Laid-Open (JP-A) No. 2-220070 discloses a process cartridge which can be used with a plurality of image formation apparatus main bodies having different process speeds and which enables the image formation process conditions thereof to be changed in accordance with the process speed of each image formation apparatus main body. In addition, JP-A No. 6-19233 discloses a process cartridge detachable from a plurality of image formation apparatuses having different process speeds and an image formation apparatus which is devised to be capable of performing appropriate exposure and the like in view of the probability that such a process cartridge is attached to the apparatus.
According to these conventional arts, however, each process cartridge is adjusted to the inherent process speed of the image formation apparatus main body. As a result, user""s demand for changing the performances of an image formation apparatus cannot be satisfied by the conventional arts, with the result that the user needs to purchase a new image formation apparatus.
It is an object of the present invention to provide an image formation unit and an image formation apparatus which can make it unnecessary to purchase another image formation apparatus main body if a user wants to have the performances of the image formation apparatus changed.
Further, one of the performances of an image formation apparatus which a user frequently wants changed is improved image quality or particularly improved pixel density (improved resolution).
It is, therefore, another object of the present invention to provide an image formation unit and an image formation apparatus which can change pixel density without the need to purchase a new image formation apparatus main body.
An image formation apparatus of such a type as to write a latent image on a photosensitive member using a writing unit which is an exposure unit has, however, a problem of the positional accuracy of the photosensitive member and the exposure unit. This problem will be explained below.
At present, as market demand for the improvement of image quality is rising, writing density is improved accordingly. Following the improved density, the diameter of a light beam for a writing of applied from an optical scanning device which serves as an exposure unit used to form a latent image on a photosensitive member, is made smaller in size (to 30 xcexcm).
According to such an optical scanning device, if the beam diameter is smaller, the depth margin of the beam diameter (which is a range which satisfies the required specifications of the beam diameter including an allowance change) is narrower at a rate of the square of a change in beam diameter. If the beam diameter is narrowed up to about 30 xcexcm, for example, the depth margin of the beam diameter is as small as about 1 mm. If so, the actual depth margin of the beam diameter is almost zero because of the accumulated processing errors of an optical element and a holding component such as a deflector and an imaging element which constitute the optical scanning device.
The irregularity of the distance between the optical scanning device and a photosensitive member which is a scanning target medium particularly has a great influence on the depth margin of the beam diameter. The distance therebetween varies from about 0.3 mm to about 0.5 mm, which irregularity occupies nearly half the depth margin of an optical system in a design phase.
For example, as shown in FIG. 24, a conventional optical scanning unit 1006 having a semiconductor laser (not shown) which serves as a light source, a deflector 1001, a plurality of lenses 1002 and 1003 such as fxcex8 lenses and a folded mirror 1004 provided at predetermined positions of a housing 1005, respectively, is provided. The holding section (not shown) of a photosensitive member 1007 which serves as an image carrier is held by the frame (not shown) of an image formation apparatus main body. Various components are arranged between the housing 1005 and the photosensitive member 1007. As a result, the processing errors, assembly errors, deformations and the like of the respective components are accumulated, thereby causing a large positional error between the optical elements and the photosensitive body 1007. Reference symbol 1008 denotes a dustproof glass.
Further, as shown in FIG. 25, the photosensitive member 1007 is sometimes arranged to be inclined with respect to the scanning line L of the optical scanning unit 1006, which eventually, probably causes an output image to be inclined.
It is, therefore, yet another object of the present invention to provide an image formation unit and an image formation apparatus wherein even if pixel density is changed without replacing an image formation apparatus main body with another one, the irregularity of the distance between a scanning optical system, which functions as a writing unit in the image formation apparatus, and an image carrier is reduced, whereby it is possible to widen a depth margin, to satisfy the desired specifications of a beam spot diameter, to reduce the degradation of image quality, to compensate for the processing errors of other optical elements and a holding member by the widened depth margin and to increase the quantity of allowances allocated to the respective components.
Another performance of the image formation apparatus which the user wants changed is shortened fixing rise time which influences print finishing speed.
It is, therefore, still another object of the present invention to provide an image formation unit and an image formation apparatus which can change fixing rise time without the need to purchase a new image formation apparatus main body.
Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.